Antenna filtering arrangement for a dual mode radio...

Details Antenna filtering arrangement for a dual mode radio... Antenna filtering arrangement for a dual mode radio...

1997-09-11

2001-02-06

Nguyen, Lee (Department: 2746)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S132000, C455S143000, C455S168100, C455S188100, C455S553100, C370S272000, C370S275000, C370S297000, C370S339000

Reexamination Certificate

active

06185434

ABSTRACT:

The invention relates to the separation of transmission and reception generally in radio transceiver devices and particularly in dual mode devices which are designed for operation in multiple radio systems.
BACKGROUND OF THE INVENTION
The Global System for Mobile Telecommunications (GSM) is currently the most widely used one of the operational digital cellular networks. Because of network congestion it has been imperative to change the operating frequency of the GSM system from the original 900 MHz, approx., to 1.8 GHz. Cellular networks complying with other standards are also widely used around the world. With the mobility of people and communication between people increasing, there is a growing need for general-purpose phones that operate in different networks according to network availability and/or service prices. In dual mode radio telecommunications, the GSM and DECT (Digital European Cordless Telephone), for example, or other systems with significantly different specifications, can operate as pairs. In dual band radio telecommunications, the systems are very much alike (e.g. GSM and PCN, Personal Communication Network), but the operating frequency of the higher-frequency system is a multiple of the lower-frequency system. The dual mode capability is also taken into account in the so-called third generation cellular systems (Universal Mobile Telecommunication System, UMTS/Future Public Land Mobile Telecommunications System, FLPMTS).
A dual mode radio communication device has to accommodate the duplexing and multiple access methods of the different systems. Duplexing means separation of traffic in the transmit direction from the traffic in the receive direction in the communication between two transceiver devices. Common methods include time division duplexing, TDD, and frequency division duplexing, FDD. Multiple access means sharing the capacity of a system or its part (a base station, for instance) between several terminals (such as mobile phones, for example). Commonly used methods include time division multiple access, TDMA, frequency division multiple access, FDMA, and code division multiple access, CDMA. In addition, the systems employ various multiplexing methods in which one device directs the transmitted information from several sources to a common transmission channel, separating the signals by means of, say, time division multiplexing, TDM, or frequency division multiplexing, FDM.
A prior art radio apparatus using full time division or frequency division duplexing includes several RF and IF filters both on the transmitter side and on the receiver side.
FIG. 1
shows a prior art GSM radio. In the GSM system, transmission and reception are carried out in different time slots and at different frequencies. The radio apparatus
100
includes on the receiver side a band-pass filter
12
the input port of which is connected to an antenna switch
14
. The output port of the filter is connected to a low-noise amplifier (LNA)
17
which amplifies the received radio signal. It is followed by a second band-pass filter
18
which further filters the received signal. The output port of the filter
18
is connected to a mixer
11
in which the received signal is mixed with a first injection signal coming from a synthesizer
22
. The mixing result, which is an intermediate-frequency signal IF, is taken via a filter
24
to a RF circuit in the receiver for further processing.
The transmitter part of the radio
100
includes a second local oscillator signal (LO)
26
which is produced by the transmitter pre-stage (not shown) and mixed in the mixer
30
with the first injection signal. The output of the mixer
30
is taken to a band-pass filter
13
which is normally found prior to the transmitter power amplifier
16
. The output of the power amplifier
16
is connected to the input of a low-pass or band-pass filter
15
so as to further filter out undesired components in the signal before transmitting it via an antenna
21
. In between the power amplifier
16
and the low-pass filter
15
there is often a directional coupler (not shown) which can be used for measuring the power level of the signal brought to the antenna.
FIG. 2
shows a DECT radio according to the prior art. A radio apparatus
200
includes a band-pass filter
19
the input port of which is connected to an antenna switch
14
. The output port of the filter is connected to an antenna
21
. One output port of the antenna switch is connected to a low-noise amplifier (LNA)
17
which amplifies the received radio signal. It is followed by a second band-pass filter
18
which further filters the received signal. The output port of the filter
18
is connected to a mixer
11
in which the received signal is mixed with a first injection signal coming from a synthesizer
22
. The mixing result, which is an intermediate frequency signal IF, is taken to a RF circuit in the receiver for further processing.
The transmitter part of the radio
200
includes a mixer
30
in which the I/Q-modulated transmission signal is mixed with an injection signal. The output of the mixer
30
is taken to a band-pass filter
13
which is normally found prior to the transmitter power amplifier
16
. The output of the power amplifier
16
is connected to a second output port of the antenna switch
14
.
The antenna switch, which connects the antenna alternately to the transmitter and receiver branches, is used in a mobile phone to separate the signals if the transmission and reception frequencies are the same. If the transmission frequency band is different from the reception frequency band, the separating unit may be a filter similar to the duplex filter used in analog phones. The latter option can also be used in systems employing frequency division multiple access.
FIG. 3
shows a prior art GSM radio
301
which differs from the radio
100
shown in
FIG. 1
in that in this apparatus
301
the antenna switch (
14
), band-pass filter (
12
) and low-pass filter (
15
) are replaced by a duplex filter
20
. The rest of the functions of these two radios are identical. A duplex filter is a three-port circuit element in which there is a receive branch filter between the antenna port and the receiver port, and a transmit branch filter between the transmitter port and the antenna port. The operating frequencies of the filters are such that a transmission-frequency signal cannot enter the receiver port and a reception-frequency signal cannot enter the transmission port. The frequency characteristics of the filters may be adjustable.
FIG. 4
shows a prior art dual mode GSM/DECT TDD radio
400
wherein both systems use a common antenna. In the radio according to
FIG. 4
the antenna filtering arrangements in both systems are based on antenna switches and separate filters. An antenna switch
41
connects the common antenna either to the GSM or to the DECT system. When choosing the DECT system, the rest of the functions of the radio are, mainly the same as those shown in FIG.
2
and comprise a band-pass filter
19
, a second antenna switch
14
b,
a receiver chain
17
b
-
18
b
-
11
b
-
24
b
and a transmitter chain
13
b
-
16
b.
When the GSM system is used the rest of the functions of the radio are mainly the same as those shown in FIG.
1
and comprise a receiver chain
12
a
-
17
a
-
18
a
-
11
a
-
24
a
and a transmitter chain
13
a
-
16
a
-
15
a
as well as a third antenna switch
14
a
which corresponds to the antenna switch
14
shown in
FIG. 1. A
switch
42
on the receive side and a switch
43
on the transmit side operate synchronously with the antenna switch
41
, connecting the radio-frequency parts of either the DECT or the GSM system shown in
FIG. 4
to the common modulation and demodulation parts of the dual mode phone and thence to other parts of the radio apparatus.
Even if a digital mobile phone using frequency duplex had an antenna switch to separate transmission and reception, it also must have filters since there has to be selectivity in the receiver input and it has to protect a low-noise preamplifier. Harmonic multiples of th

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